1. Technical Field
The present invention relates to the area of light wave guide technology. It relates to a procedure for attaching a light wave guide in a connector for an optical plug-in connection according to the introductory clause of claim 1.
Such a procedure is known from publication U.S. Pat. No. 4,790,622, for example.
The application also relates to an adhesive for use in such a procedure.
2. Prior Art
Two-component epoxy adhesives are generally used to bond optical light wave guides, in particular light wave guide cables, with corresponding connectors. Depending on the type of manufacture, use is made of adhesives of this kind with a long xe2x80x9cpot lifexe2x80x9d. To achieve a reasonable cycle time under these preconditions while manufacturing the adhesive bond, post-curing with the application of heat must take place. However, it is also conceivable to use two-component adhesives with a short pot life, which reach the desired strength at room temperature within 10-20 minutes. However these two-component adhesives must be prepared several times a day, i.e., mixed together out of several separately prepared components.
In addition to these epoxy adhesives, recent times have seen the development of acrylate-based adhesives, and their increasing use in xe2x80x9con sitexe2x80x9d packaging, meaning outside the manufacturing facility, i.e., at the assembly site. These acrylate adhesives are easier to handle. Even though they also consist of two components, they offer the advantage of very short reaction times. However, the storage stability of the products is very limited at temperatures exceeding 40xc2x0 C. Since temperatures of up to 60xc2x0 C. are easily reached in the unit load under the tarpaulin during transport by truck in the summer after 2 hours of exposure to direct sunlight, the application of such highly reactive adhesive systems is clearly limited.
For example, another patent of the applicant (CH-A5687621) describes bonding a light wave guide into the ferrule of an optical plug-in connection by means of an adhesive consisting of two components. One of the two components, which each consist of unsaturated compounds dissolved in mono- and/or multifunctional acrylates, is accommodated in the bore hole of the ferrule for this purpose. The light wave guide is wetted with the other component before introduced into the bore hole. During insertion, a boundary layer reaction gives rise to polymerization within a few minutes. The prefilled ferrules require special facilities, however. In addition, the component in the ferrule might in some circumstances become unusable under unfavorable storage conditions, as a result of which the ferule itself, which is the most valuable component of the plug-in connector due to the highly precise ceramics used, becomes unusable.
Also known are connectors/plugs that are filled with a hot-melt-type adhesive. These connectors are heated on site in a heater, and the light wave guide is introduced in a hot state. Work can then continue after cooling. The disadvantage to this adhesive system is that the adhesive, which is solid in a cold state, softens again at elevated temperatures, and cannot be used everywhere given this limited temperature resistance.
A similar solution, in which a solid, multi-component reaction adhesive is used instead of a melt adhesive, in which the adhesive is liquefied via heating, thereby initiating a hardening reaction, is known from the U.S. Pat. No. 4,790,622 mentioned at the outset. The disadvantage here is that the connector as a whole becomes no longer useable once the reaction adhesive therein has exceeded its shelf life or has been degraded by external factors.
A composite adhesive for optical and optoelectronic applications is described in DE-A1-195 12 427. The adhesive is present as a liquid dispersion, and is therefore less suitable for outside use.
Another solution that does completely without adhesives would be mechanical fixation, in which mechanical means are used to laterally press on the fibers lying in the connector. Since a high lateral pressure would be necessary to immovably fix the fibers, the fibers could deform after a longer period of time. Such a deformation would result in the diminished performance or complete failure of the light guide.
Therefore, the object of the invention is to indicate a procedure for attaching a light wave guide in a connector that avoids the disadvantages of known procedures, and in particular can be performed easily and simply at the assembly site, and that is distinguished by a very good storability and low temperature sensitivity on the part of the means used.
The object is achieved via the totality of features in claim 1.
The use of a solid reaction adhesive as described in the invention, which only reacts when transformed into a liquid state (melted or dissolved), and then goes over into a thermoset state, eliminates the mixing of the adhesive, and makes the completely hardened (cured) adhesive compound comparatively insensitive to later temperature increases. However, it is particularly advantageous that the solid reaction adhesive can be stored especially well and long prior to its use without loosing its adhesive power. The powdery adhesive has the special property of being free-flowing and very easily moveable, as long as the adhesive is fully functional, but that it is baked or sintered together into a solid mass once it has lost its adhesive power. The use of a powdery adhesive also has the particular advantage that simply shaking the adhesive container makes it possible to determine whether the adhesive is still usable, which is not possible for other adhesive systems.
A first preferred embodiment of the procedure described in the invention is characterized by the fact that the receptacle is brought to and maintained at a temperature greater than or equal to the melting point of the adhesive, and that the light wave guide is introduced into the bore hole of the heated receptacle with the adhering particles. The special advantage to this is that no other additional chemical agents must be prepared for performing the bonding process. Rather, the adhesive reaction is initiated through a simple (controlled) temperature increase.
The adhesion of the powdery adhesive to the light wave guide, which can probably be attributed to electrostatic forces of attraction or surface forces, surprisingly causes precisely the correctly metered amount of adhesive (a few mg) to be transferred into the bore hole, and hence to the bonding location. This automatically and easily avoids disrupting excess amounts of adhesive at the bonding location.
Another preferred embodiment of the procedure according to the invention is characterized by the fact that the adhesive is transformed into the liquid state by adding a solvent, that the light wave guide is first immersed into the solvent with its one end, and that the light wave guide is subsequently immersed in the powdery adhesive with its one end. The solvent dissolves the reactive components in the reaction adhesive, causes them to start reacting with each other. A special metering of the solvent is here not necessary. While the solvent must be kept additionally available and applied in this case, a heater need not be used.
One particularly good and stable bond arises when using a receptacle with a bore hole whose inside diameter is only slightly, preferably 0.002 to 0.008 mm, larger than the outside diameter of the light wave guide according to another preferred embodiment of the procedure described in the invention. If the adhesive is transformed into the liquid state through heating, the adhering powdery adhesive is stripped from the light wave guide during insertion of the light wave guide into the bore hole due to the slight diameter tolerances, comes into contact with the heated receptacle, melts open, and is then drawn into the gap between the light wave guide and receptacle as a (relatively low-viscosity) liquid, to subsequently be hardened. At the same time, the light wave guide is effectively guided into the bore hole before hardening. In this case, excessive stripped particles of adhesive can accumulate in the funnel-shaped opening of the borehole without the danger of falling off, and form a melt bath enveloping the light wave guide, from which enough liquid adhesive can always be drawn into the gap when introducing the light wave guide into the bore hole.
The adhesive according to the invention intended for use in the procedure described in the invention is characterized by the fact that the adhesive is a two-component reaction adhesive, and that the adhesive essentially consists of a solid, preferably a crystalline, resin, to which is added a solid aid for curing purposes.
One preferred embodiment of the adhesive is characterized by the fact that the solid resin is selected from among the group of unsaturated polyester resins, the solid acrylate resins, the methacrylate solid resins and epoxy solid resins, and that a peroxide, e.g., an amine adduct for the epoxy resins, is used as the curing aid for the polyester, acrylate and methacrylate resins.
One preferred further development of this embodiment is characterized by the fact that a (1.1-di(tert.butylperoxide)3.3.5-trimethylcyclohexane 40% on chalk) is used as the peroxide, that the adhesive is present in powder form, that a separating agent is added to the powdery adhesive, preferably in the form of a colloidal silica, and that a pigment, preferably a red iron oxide, is mixed in with the powdery adhesive, for better monitoring the bonding process. The separating agent receives the free-flowing properties, and prevents a reaction between the components before melting takes place. The pigment makes it possible to easily track the melting and reaction process visually.
In a first further development, a polyester resin based on terephthalic acid is used as the unsaturated polymer resin, and the adhesive is composed of 89% polyester resin, 6% 1.1-di(tert.butylperoxide) 3,3,5-trimethylchclohexane 40% on chalk, 3.5% colloidal silica and approx. 1.5% iron oxide.
In a second alternative further development, the solid resin is a mixture of methacrylamide and bisphenol A-dimethacrylate, and the adhesive consists of 80% methacrylate, approx. 9% bisphenol A-dimethacrylate, approx. 6% 1.1-di(tert.butylperoxide) 3.3.5-trimethylcyclohexane 40% on chalk, approx. 1.5% iron oxide.
In a third alternative further development, the solid resin is an epoxy resin, and the adhesive consists of 50-70% epoxy resin, 20-40% epoxy adduct, 5-10% colloidal silica and approx. 1.5% iron oxide.
Additional embodiments are derived from the subordinate claims.